Did you may have found a bug in Joomla! 3.x but aren't sure? This forum is the place to help figure out if the problem is a bug and how to report it. If you are an experienced Joomla! user and are certain that you have found a bug please use the Bug Tracker to submit your issue. This forum is for discussion about bugs and to get help with reporting them to the Bug Tracker: https://issues.joomla.org

That's not a valid 'solution' because that file will be overwritten when the core is updated. You'll need to write a plugin or a method using JModelLegacy in your template to achieve the goal and avoid overwrite.

Something like this (not a working method, just a clue where to search for a solution)

I think this is the bug. Because of the code $this->getState('filter.tag') will get filter tag from menu to other menu. If you create menu with default category and category menu with any tag. You will receive empty page after select tag category menu.